Because of its wind facilitated pollination behavior, switchgrass is typically characterized as an obligate outcrosser (Martinez-Reyna and Vogel 2002). Although homozygous inbred lines of switchgrass had not been reported yet, some studies indicated that the ratio of self-pollination was high in some specific genotypes (Casler et al. 2011; Liu and Wu 2012a). Through continuous selfing, development of inbred lines is possible, which will enable to produce single cross hybrid cultivars in switchgrass to increase biomass yield (Casler et al. 2011; Aguirre et al. 2012; Liu and Wu 2012a; Liu et al. 2013a). Morphological traits, such as pubescence on the adaxial surface of the leaf blade, foliage color, and seed size, were used to identify selfed and crossed progeny in previous experiments (Martinez-Reyna et al. 2001). However, they are not only genotype-dependent but also may be environmentally sensitive. In contrast, molecular markers have many advantages and have been used for identification of selfed progeny. Liu and Wu (2012a) adopted 12 SSR markers to test the selfed progeny of a genotype, and found the percentage of selfing ratio reached 61.2. Todd et al. (2011a) used six SSR markers and reported the confirmation of selfed progeny in switchgrass. Recently a genome-wide multiple duplex-SSR protocol was established, which was used for the identification of switchgrass selfed progeny in different growth conditions (Liu and Wu 2012b). These results indicate molecular markers are powerful in switchgrass breeding.

Perspectives

Although vast genetic variations of switchgrass have been revealed by molecular markers, the species is still an undomesticated organism with great potential for improvement of agronomic and biofuel traits (Casler

2012) . Genetic dissection of bioenergy-related traits is a critical step in breeding switchgrass. It is expected a large amount of data on associations between markers and sequences with economically important traits will be published in the near future from the current ongoing projects. However, little work is conducted to identify genes related to molecular mechanism of biomass development in switchgrass. Map-based-cloning of QTL and associate mapping can be utilized to isolate target genes and elucidate basic molecular mechanisms in the future. At the same time, the identification of easily-used molecular markers that are tightly linked or co-segregating with bioenergy-related traits will greatly accelerate breeding progress for enhancing biomass production and processing traits via marker assisted selection and advanced breeding procedures.

Acknowledgements

The writing of this chapter is partially supported by the National Science Foundation award EPS 0814361.